After water reaches its boiling point, it becomes moist steam that is a mixture of water vapor gas (the gas phase part: saturated vapor) and water droplets (the liquid phase part: saturated water). Here the weight ratio of the water vapor gas relative to the moist steam is termed the “dryness fraction.” For example, if water vapor gas and water droplets exist at half each, then the dryness fraction would be 0.5. Moreover, when there are no water droplets but instead there is only water vapor gas, then the dryness fraction would be 1.0. From the perspective of efficiency of use of the apparent heat and latent heat within the moist steam in heat exchanging equipment, and the like, from the perspective of preventing corrosion of turbine blades in steam turbines, and so forth, it is desirable that the dryness fraction of the moist steam be brought to near 1.0. Because of this, a variety of methods have been proposed whereby to measure the moist steam.
For example, Japanese Unexamined Patent Application Publication 8-312908 (JP '908) discloses a technology for calculating the dryness fraction by calculating the saturated hydraulic entropy and the saturated steam entropy using a saturated steam table based on the dry steam flow rates and pressures before and after a pressure regulating valve, taking advantage of the fact that there is no change in total entropy across a pressure regulating valve that is disposed in a pipe.
However, in the technology disclosed in JP '908, it is necessary for the time constant for the sensor for detecting the flow rate and pressure of the moist steam to be long, and necessary to cause the moist steam that is to be measured to undergo a state change from the two-phase state to the gas phase state, and also necessary to stabilize, in the gas phase state, that which is to be measured, and thus there is a problem in that measuring the dryness fraction is time-consuming. Because of this, while it is possible to measure the dryness fraction when the moist state is in a steady state, this cannot be applied to measuring the dryness fraction when the moist steam is in a transient state, prior to becoming stable.
Given this, one aspect of the present invention is to measure the dryness fraction when the moist steam is in a transient state.
Note that there is no limitation to this aspect, but rather enabling means of resolution having the principle of resolution illustrated in the examples below is positioned as another aspect of the present invention.